Kindermama, have hope. For the most part our family is a very happy one except for a few little things. Granted, our children are young, but I feel like good things are worth fighting for. I have to say that I grew up in a blended family and to this day I still consider my stepdad my "real dad". He was the one that was there when I needed him. Have you considered family counseling? I do not know the whole story but kids will be kids. If its your SO that is causing the problems, then some heart-felt talks are what is needed. If he cares for you, he will listen to your fears and concerns and try to make things work.
We also live by this philosophy - God first, husband or wife second, and children third. If things are not right between you and your SO, it is very hard to fix your children. When I first heard this, I was disbelieving. How could I ever put anyone before my helpless, young son? But I realized that it is a big puzzle and you have to put some pieces in place before others will fit.
Good luck and keep trying. That is what is most important.